Bulletin d’avalanche

Flathead Range & Glacier NP

Flathead Avalanche Center
Voir sur la carte

Danger d’avalanche

Thu
Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
1 · Faible
Open full map
Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The danger remains elevated on steep slopes where you can trigger loose dry sluffs and soft slabs of drifted snow. As new snow falls and blows, use small test slopes to see how well new snow is bonding to the low density snow, crusts, and weak facets underneath. Avalanches will become more likely on steep slopes as new snow accumulates and you see red flags like blowing snow, cracking, and natural sluffing throughout the day.

Problèmes avalancheux

  • Loose Dry

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Dry sluffs will become larger and more likely as more snow accumulates on very steep sheltered slopes throughout the day. You can manage the risk of getting carried or buried by fast-moving loose snow by avoiding confined chutes. Ride slopes with room to maneuver and let the sluff pass you by, or choose lower angled terrain to avoid the problem completely.

    (3/23/2021) Loose snow avalanches were easy to trigger. They were more dangerous where they could run far distances and entrain more snow.

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    New snowfall moves into the region by late morning accompanied by moderate ridgetop winds. These winds will be the driving factor in new slab formation on steep leeward terrain. The danger of triggering slabs of drifted snow will increase throughout the afternoon and evening. Use small test slopes and hand pits to see how well denser, textured slabs are bonding to underlying surfaces. Shooting cracks below ridgelines and on the downwind sides of gullies and rollovers are early warning signs that drifts are becoming sensitive. Plan to avoid steep leeward slopes where you see blowing snow.

    (2/25/2021) Wide-breaking wind slabs

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Unlikely
    Taille
    2–3

    Although it is unlikely, it is not impossible to trigger a very large hard slab avalanche failing 2 to 6 feet deep on shaded aspects above 6500 feet. Stick to slopes less than 35 degrees if you do not feel a supportable crust in hand pits under the new and recent snow. Avoid slopes near rocky outcrops, with variable snow cover, or with cornices overhead. Cornice fall or a smaller avalanche can be the trigger that sets off a destructive slide. The last reported avalanche failing on mid-winter weak layers was over a week ago. Though the potential consequences of being caught by surprise should keep the hazard in the back of your mind.

    (3/17/2021) The crown from a hard slab avalanche that's more than a few days old.

Avalanche Discussion

Small to large, natural and triggered, soft slabs and sluffs ran across the region starting Monday. The sun triggered many of these on northeast to east to southeast aspects on Tuesday. South and westerly slopes saw a round of wet loose avalanches Tuesday afternoon.

New snow begins by mid-Wednesday favoring the Swan and northern Whitefish ranges. It will fall on 4 to 12 inches of loose, low-density snow near and above treeline on shady aspects and on a melt-freeze crust on slopes that saw the most warming on Tuesday. Snowfall rates and ridgetop winds may be enough to thicken the new snow into slabs by Wednesday afternoon and into Thursday morning.

The snow from the past several days rests on a slick crust to about 6,500 feet, old wind slabs near and above treeline, or near surface facets. 

Deeper in the snowpack, mid-winter weak layers sit 2 to 6 feet deep. These layers have been unreactive for more than a week. A large cornice fall or smaller avalanche could trigger a hard slab on one of these layers. 

Glide cracks litter steep east to south to southwest-facing slopes above about 5,500 feet. New snow may make them difficult to see. It’s best to avoid slopes near and below them. 

Régions couvertes